Corona charging process and apparatus in electrophotography

ABSTRACT

The method of corona charging comprising a main corona discharging electrode positioned to act upon an insulating layer on an electroconductive supporter which is not earthed, and corona discharge electrodes of a polarity opposite to said main electrode positioned to simultaneously act with said main electrode upon a portion of the electroconductive supporter. In the structure of photographic material comprising the conductive layer on highly insulated supporter, it is difficult to earth the conductive layer.

United States Patent n 1 Sato Feb. 6, 1973 [54] CORONA CHARGING PROCESS AND Primary Examiner-L. T. Hix

" APPARATUS IN Att0mey-Gerald .l. Ferguson, Jr.

ELECTROPHOTOGRAPHY [75] Inventor: Masamichi Sato, Asaka, Japan [57] ABSTRACT The method of corona charging comprising a main [73] Asslgnee FUJI Photo corona discharging electrode positioned to act upon Kanagawa, Japan an insulating layer on an electroconductive supporter [221 Filed: April 14, 1971 which is not earthed, and corona discharge electrodes of a polarity opposite to said main electrode posi- [21] Appl' 133787 tioned to simultaneously act with said main electrode upon a portion of the electroconductive supporter-In [52] US. Cl. ..317/262 A, 355/l7 the structure of photographic material comprising the [51] Int. Cl. ..G03g 15/02 conductive layer on highly insulated supporter, it is [58] Field of Search ..3 1 7/262 A; 355/ l 7 difficult to earth the conductive layer.

I 56] References Cited 10 Claims, 6 Drawing Figures UNITED STATES PATENTS 3,543,023 11/1970 Yellin et al. ..3l7/262 A 34 30 34 r 3 3131 33 736 36 ,1 l1 t L i 35 2 J i 35 38 38 PATENTEUFEB 6 I975 3.715 40 FIG. 12

1; W T n FIG.3

5|2 2' no.5 g

' INVENTOR MASAMICHI SATO ATTOR NEYJ'.

CORONA CHARGING PROCESS AND APPARATUS IN ELECTROPHOTOGRAPHY This invention is useful to charge the photographic material having the structure such as above mentioned.

If a polyester base evaporated aluminum or a resin coated paper be used as a supporter in future, this invention will be useful.

BRIEF EXPLANATION OF THE DRAWING DETAILED DESCRIPTION OF THE INVENTION This invention relates to a novel charging process and apparatus in electrophotography.

Generally, an electrophotographic material'has a photoconductive insulative layer or a non-photoconductive insulating layer formed on an electroconductive base. Typical examples include a metal plate having photoconductive selenium layer deposited in vacuum evaporation thereon and a paper sheet coated or impregnated with an electroconductive polymer and additionally coated with what is obtained by blending a photoconductive zinc oxide powder with an insulating resin. It is a general practice to have such conventional electrophotographic material electrically charged by means of corona'discharge, for example.

FIG. 1 is a sectional view illustrating a conventional method of charging generally adopted. In FIG. 1, l denotes an electrophotographic material having a photoconductive insulating layer 12 formed on a conductive base 11 such as of a metal plate. Denoted by 13.

is a corona wire stretched several centimeters above I the photoconductive insulative layer. The corona wire is covered in three directions with a shield case 14. Negative high potential is applied to the corona wire, for example, while the shield case and'the electroconductive base 11 are kept ground. When a voltage of 6 KV to 7 KV is applied to the corona wire which is held at a distance of several centimeters from the shield case 14, the corona wire ejects negative corona ions toward the photoconductive insulating layer, causing the photoconductive insulating layer to be charged negatively. Uniform charging of the entire surface of the photoconductive insulating layer can be accomplished by moving the corona discharge electrode unit consisting of the wire and the shield case at a fixed rate in the direction of the arrow mark or by causing the electrophotographic material to move at a fixed rate in the direction opposite to the arrow mark. The so-called double-corona charging method whereby theopposite surface of an electrophotographic material are charged by means of corona discharges of mutually opposed polarities is also known to the art. So far as the electrophotographic material is of the type formed simply on an electroconductive base as illustratedin FIG. 1, satisfactory results can be obtained by the charging method shown in FIG. 1 or the charg ing method utilizing the double-corona principle. In the case, of an electrophotographic insulating material which has an electroconductive layer 22 formed'on a highly insulating base 21 and a photoconductive insulating layer 12 additionally formed thereon, however, the electric charging method illustrated in FIG. I or resorting to the double-corona principle proves impracticable by the cross section shown in FIG. 2. The reason is that the electroconductive layer 22 is not grounded. This problem is particularly serious when the highly insulating base is made of a plastic film such as of polyester, polyethylene, polypropylene, polyvinyl chloride, or triacetyl cellulose. Where the case 21 is made of ordinary paper, since the base, though highly insulating in itself, absorbs water from the ambient air and consequently has its insulating capacity heavily degraded as compared with a base made of the aforementioned plastic film, a certain extent of grounding can be achieved by bringing the case 21 into contact with the conductor. Thus, this base can be electrically charged to an extent practically free from any serious obstacle. Where the base 21 is made of such extremely highly insulating material as polyester, however, electroconductive layer 22 is no longer grounded even if the electrophotographic material 20 is placed on the conductor. Thus, the photoconductive insulating layer is scarcely charged by a method like the one shown in FIG. 1. When the base 21 very thin andthe electroconductive layer 22 is highly conductive as in the case of a metal film made by vacuum evaporation, if corona discharge is effected downwardly on the electrophotographic material 20 which is placed on a grounded conductor, sparks are generated between the electroconductive layer 22 and the grounded conductor and the sparks serve to establish grounding. However, the grounding .by means of suchsparks is not desirable because the consequent charging potential of the photoconductive insulating layer is not consistent and the photoconductive layer is sensitive to the light emanating from the sparks. Sparks are also dangerous. When the electroconductive layer 22 is made of copper iodide, conductive carbon or conductive polymer and therefore is not so electroconductive as that made of a metal, sparks are not generated and substantially no charging is effected consequently.

For electrically charging an electrophotographic material of the construction like the one shown in FIG. 2, there has heretofore been adopted a practice of removing a side edge portion of the photoconductive layer from the electrophotographic material so as to expose the electroconductive layer and having the exposed portion grounded as required. However, the preparation of such electrophotographic material that has the electroconductive layer exposed only at the side edge portion has proved defective in that the process of manufacture becomes complicated and the grounding becomes imperfect when the electroconductive layer has insufficient conductivity.

The present invention provides a novel chargin process and apparatus which is suitable for effecting desired charging of electrophotographic materials having a-construction as illustrated in FIG. 2.

The charging process according to the present invention is characterized by disposing at least two corona discharge electrodes above a photoconductive insulative layer or an insulating layer which is formed on an electroconductive layer, one of the said electrodes being used for effecting discharge to a polarity with the surface to be charged is desired to be charged and another thereof being used for effecting discharge to a polarity opposite thereto in the area other than the area to be charged to the aforementioned polarity of discharge.

FIG. 3 is a sectional view of one preferred embodiment of the device for working the charging process according to the present invention. Numeral denotes a main discharge unit, which comprises a corona wire 31, a shield case 32 and an insulating element 33 for supporting the corona wire. An auxiliary discharge unit denoted by 34 comprises a corona wire 35 and a shield case 36. The wires 31 and 35 are disposed so as to make a right angles. The wire 31 is parallel to the plane of the drawing and the wire 35 is perpendicular to the plane of the drawing. Desired charging of the surface being processed for charging may be accomplished by causing the main discharge unit to travel in the direction perpendicular to the plane of the drawing or by causing the electrophotographic material to travel in the direction perpendicular to the plane of the drawing while keeping the dischargeunit at a fixed position. The area denoted by 37 in the diagram is an area to be charged and therefore corresponds to the range utilized effectively. The area denoted by 38 is the area of the electrophotographic material to be used wastefully. When the surface (being processed) is desired to be charged to negative polarity, negative high potential is applied to the corona wire 31 and positive high potential to the corona wire 35 respectively. When the surface is desired to be charged to positive polarity, the polarity relationship of the potentials applied to the corona wires is reversed.

Now the principle of the present invention is described by referring to the diagram of FIG. FIG. 4 shows an example using an N type photoconductive insulating layer such as a layer made of a mixture of a photoconductive zinc oxide with an insulating resin. In the diagram, 40 is a main discharge unit, 41 is an auxiliary discharge and 42 and 43 are their respective corona wires. When negative high potential (6 KV, for example) is applied to the corona wire 42 and positive high potential (+6 KV) to the corona wire 43, the corona wire 43 ejects positive corona ions toward the photoconductive layer, with a result that the ions will be deposited on the surface of the photoconductive layer. Since the photoconductive layer 12 is of N type,

it permits free movement of electrons. Consequently, free electrons (indicated by the symbol in the diagram) gather here and tend to neutralize the positive electric charge. As a result, positive electric charge (indicated by the symbol in the diagram) remains in the electroconductive layer 22, permitting negative corona ions to fly from the corona wire 42 easily to the surface of the photoconductive layer. This means that there has been obtained the effect of grounding. It has been shown experimentally that, when the magnitude of electric charge conferred on the photoconductive layer 12 by the corona wire 42 in the absence of potential application tothe corona wire 43 is regarded as unity, the magnitu de of electricjeharge conferred thereon is 100 to 800 where the potential of an equal degree in the opposite polarity is applied to the corona wire 43.

FIG. 5 is another example of the device for working the present invention, wherein 50 is a main discharge unit and 51 is an auxiliary discharge unit. The auxiliary discharge unit is disposed at a portion close to the side edge of the electrophotographic material so as to minimize possible loss of the electrophotographic material.

It is permissible to dispose auxiliary discharge electrodes 51.and 51 facing in the direction of the electroconductive layers exposed at both edges of the elec trophotographic material as illustrated in FIG. 6.

Corona discharge electrodes of a needle-shape or stripshape may be used in place of those of a wireshape.

If the corona ions ejected from the main discharge electrode and those from the auxiliary discharge electrode are suffered to overlap on the surface to be charged, the magnitude of consequent charging is decreased and inconvenience the operation. It is, therefore, desirable to provide a partition wall between the two discharge units. One shield plate may be used concurrently as such partition wall. Use of an insulating plate for this partition serves to provide a clear demarcation between the zone to be charged and the zone not to be charged.

Needless to mention, the electric charging process according to the present invention can be applied to the case in which electric charging is effected efficiently on an ordinary electrophotographic material 10 as illustrated in FIG. 1.

Now, some working examples of the present invention are cited below.

Example I An electrophotographic material was prepared by spreading an electroconductive paint (Dotite Paint .S-3S, tradename for Fujikura Chemical Co.'s product made by blending an electroconductive carbon powder with a resin) to a thickness of lp. after dried on an art paper p. in thickness and additionally spreading a mixture consisting of I00 parts by weight of a photoconductive zinc oxide powder and 20 parts by weight of an insulating resin (Styresol 4400, trade name for Japan Reichhold Co.'s styrenated alkyd resin) to a dried thickness of about 7p. thereon.

In a dark place, the resultant electrophotographic material was placed on a highly insulating plate (aboard of polyvinyl chloride resin l0 mm in thickness) and a corona discharge unit like the one illustrated in FIG. 3 was disposed thereover. In this unit was employed a main discharge unit as described below.

The corona wire was placed so as to provide an interval of 15 mm from the surface to be charged. The distance from the corona wire to the shield case was l5 mm. The wire was 0.05 mm in diameter and 300 in length. The distance from the lower edge of the shield case to the surface to be charged was 8 mm. The wire was made of tungsten. In the auxiliary discharge unit, the distance from the corona wire to the surface to be charged was I0 mm, the distance from the shield case to the corona wire was l5 mm, the wire was 0.05 mm in diameter and 50 mm in length, the distance from the lower edge of the shield case to the surface to be charged was 2 mm and the wire was made of tungsten. A potential of 6 KV was applied to the main discharge electrode and another potential of +7 KV to the auxiliary discharge electrode and the electrophotographic material was caused to travel at a rate of 50 mm per sec. In the direction perpendicular to the main discharge electrode (in the direction perpendicular to the plane of the drawing). With the exception of both end portions, the electrophotographic material was charged uniformly to a surface potential of l80 V. The zone below the auxiliary discharge electrode was left uncharged. Similar results were obtained by using an aluminized paper as an electroconductive layer in place of a paper coated with an electroconductive paint or by spreading an electroconductive polymer (such as Calgon Conductive Polymer 261 made by Calgon Co. of US.) in place of an electroconductive paint.

Example 2 An electrophotographic material similar to that used in Example 1 was placed on an insulating plate similarly to the case of Example 1 and two needle electrodes were disposed thereover at right angles with reference to the surface to be charged. The two needles were spaced by a distance of l80 mm. Of the two needles, one (maindischarge electrode) was positioned above the, center of the surface to be charged and the other (auxiliary discharge electrode) positioned above the edge portion of the surface. The forward end of the main discharge electrode was 70 mm and that of the auxiliary discharge electrode was mm respectively from the surface to be charged. A potential of l0 KV was applied to the main discharge electrode and another of +4 KV to the auxiliary discharge electrode. When the electrophotographic material was caused to travel at a rate of 30 mm/sec under the two electrodes, there was acquired a surface potential of l 50 V at the center of the surface being charged.

Example 3 The same main discharge unit that was used in the aforementioned Example I was disposed as illustratedmaterial to the corona wire was l0 mm, the distance from the shield case to the corona wire was mm, the lower forward end 62 of the shield case was 1 mm from the side edge of the electrophotographic material and the upper forward end 63 thereof was 10 mm from the side edge respectively. The auxiliary discharge electrode was 300 mm in length. A potential of -6 KV was applied to the main discharge electrode and another potential of +6 KV to the auxiliary discharge electrode respectively. The main discharge electrode was caused to travel at a rate of 50 mm/sec while both auxiliary discharge electrode and the electrophotographic material were held motionless. The surface thus processed was charged uniformly to a surface potential of-l60 V substantially throughout the entire surface.

, Example 4:

In the device of Example 3, a needle electrode was used as the auxiliary discharge unit. The main and auxiliary discharge electrodes were caused to travel while the electrophotographic material was kept motionless.

The distance from the forward end of the auxiliary discharge electrode to the side edge of the electrophotographic material was 10 mm. A potential of -6 KV was applied to the main discharge electrode and another potential of +6 KV to the auxiliary discharge electrode. The surface thus processed was charged uniformly to a surface potential of -l 60 V substantially throughout the entire surface.

Example 5 As an electrophotographic material, there was used an aluminum plate having photoconductive selenium layer deposited by vacuum evaporation thereon to a thickness of 25 p.. Two needles were disposed at a distance of 100 mm above the selenium plate. The forward end of each needle was 50 mm from the selenium plate. Potentials of +3 KV and -3 KV were applied to the two needles for l0 seconds. The selenium plate was mounted on an insulating plate and the aluminum base was not grounded. After application of the potentials, the portion of the selenium plate below the needle of positive polarity was charged positively and the portion thereof below the needle of negative polarity was charged negatively. When the selenium plate charged to positive and negative polarities as mentioned-above was exposed to light through an image and subsequently developed by using a two-component developing agent consisting of a carrier having glass beads coated with ethyl cellulose and a toner produced by pulverizing a mixture of polystyrene and carbon black, a positive image was formed in the positively charged area and a reversed image in. the negatively charged zone.

Example 6 There was used an electrophotographic material which was prepared by spreading Calgon Conductive Polymer 261 (trade name) to obtain the layer of 1.5 V

. material comprising a highly insulating base and a conductive layer, which some conventional charging processes have failed to accomplish and others have managed to accomplish while involving many difficulties, can now be accomplished efficiently by the present invention. It goes without saying that the charging process of the present invention can be utilized for electric charging of an ordinary electrophotographic material having an insulating layer formed on an electroconductive substrate.

. What is claimed is:

l. A corona charging process, in electrophotography characterized by simultaneously operating a main I corona discharge electrode and an auxiliary corona discharge electrode, said main corona discharge electrode charging one portion of the surface of an electrophotographic member having a photoconductive layer or an insulating layer formed on an electroconductive layer to a desired polarity and the said auxiliary corona discharge electrode of the opposite polarity charging another portion of the surface or edge portion of said electrophotographic member to said opposite polarity whereby the electrophotographic member is electrically charged without grounding the aforementioned electroconductive layer and without any air or dielectric breakdown occurring between said auxiliary electrode and said electroconductive layer.

2. A corona charging process as claimed in claim 1 wherein the main corona discharge electrode charges almost all of the surface of the electrophotographic member and the auxiliary electrode charges the edge portion of the surface or side edge of the member.

3. A corona charging apparatus in electrophotography, comprising a main corona discharge electrode confronting the surface of an electrophotographic member having a photoconductive layer or an insulating layer to be charged to a desired polarity formed on an electroconductive layer and an auxiliary corona discharge electrode of the opposite polarity confronting another portion of the surface or edge portion of said electrophotographic member for charging said another portion or edge portion to said opposite polarity so that the electrophotographic member is electrically charged without grounding the electroconductive layer and without any air or dielectric breakdown occurring between said auxiliary electrode and said electroconductive layer.

4. An apparatus as claimed in claim 3 wherein said main and auxiliary corona discharge electrodes are both wire electrodes, said main electrode being parallel to the surface of the electrophotographic member, said auxiliary electrode being parallel to the dge of the member, and said electrophotographic member being adapted to be carried along and adjacent said auxiliary I corona discharge electrode.

5. A process as in claim 1 where said photoconductive layer or said insulating layer is doped to readily permit the movement of charge carriers of said desired polarity whereby said charge carriers tend to neutralize the said charge of opposite polarity on the electrophotographic member so that charge of said opposite polarity remains in said electroconductive layer thereby effectively grounding the electroconductive layer for the charge of desired polarity.

6. A process as in claim 1 where said electrophotographic member includes an electrically insulative base upon which said electroconductive layer is disposed.

7. A process as in claim 1 where said electroconductive layer is unconnected to any source of electric potential.

8. Apparatus as in claim 3 where said photoconductive layer or said insulating layer is doped to readily permit the movement of charge carriers of said desired polarity whereby said charge carriers tend to neutralize the said charge of opposite polarity on the electrophotographic member so that charge of said opposite polarity remains in said electroconductive layer thereby effectively grounding the electroconductive layer for the charge of desired polarity.

9. Apparatus as in claim 3 where said electrophotographic member includes an electrically insulative base upon which said electroconductive layer is disposed.

.10. Apparatus as in claim 3 where said electroconductive layer is unconnected to any source of electric potential. 

1. A corona charging process, in electrophotography characterized by simultaneously operating a main corona discharge electrode and an auxiliary corona discharge electrode, said main corona discharge electrode charging one portion of the surface of an electrophotographic member having a photoconductive layer or an insulating layer formed on an electroconductive layer to a desired polarity and the said auxiliary corona discharge electrode of the opposite polarity charging another portion of the surface or edge portion of said electrophotographic member to said opposite polarity whereby the electrophotographic member is electrically charged without grounding the aforementioned electroconductive layer and without any air or dielectric breakdown occurring between said auxiliary electrode and said electroconductive layer.
 2. A corona charging process as claimed in claim 1 wherein the main corona discharge electrode charges almost all of the surface of the electrophotographic member and the auxiliary electrode charges the edge portion of the surface or side edge of the member.
 3. A corona charging apparatus in electrophotography, comprising a main corona discharge electrode confronting the surface of an electrophotographic member having a photoconductive layer or an insulating layer to be charged to a desired polarity formed on an electroconductive layer and an auxiliary corona discharge electrode of the opposite polarity confronting another portion of the surface or edge portion of said electrophotographic member for charging said another portion or edge portion to said opposite polarity so that the electrophotographic member is electrically charged without grounding the electroconductive layer and without any air or dielectric breakdown occurring between said auxiliary electrode and said electroconductive layer.
 4. An apparatus as claimed in claim 3 wherein said main and auxiliary corona discharge electrodes are both wire electrodes, said main electrode being parallel to the surface of the electrophotographic member, said auxiliary electrode being parallel to the dge of the member, and said electrophotographic member being adapted to be carried along and adjacent said auxiliary corona discharge electrode.
 5. A process as in claim 1 where said photoconductive layer or said insulating layer is doped to readily permit the movement of charge carriers of said desired polarity whereby said charge carriers tend to neutralize the said charge of opposite polarity on the electrophotographic member so that charge of said opposite polarity remains in said electroconductive layer thereby effectively grounding the electroconductive layer for the charge of desired polarity.
 6. A process as in claim 1 where said electrophotographic member includes an electrically insulative base upon which said electroconductive layer is disposed.
 7. A process as in claim 1 where said electroconductive layer is unconnected to any source of electric potential.
 8. Apparatus as in claim 3 where said photoconductive layer or said insulating layer is doped to readily permit the movement of charge carriers of said desired polarity whereby said charge carriers tend to neutralize the said charge of opposite polarity on the electrophotographic member so that charge of said opposite polarity remains in said electroconductive layer thereby effectively grounding the electroconductive layer for the cHarge of desired polarity.
 9. Apparatus as in claim 3 where said electrophotographic member includes an electrically insulative base upon which said electroconductive layer is disposed. 